Method and apparatus for determining flow velocity in a channel

ABSTRACT

An ultrasonic flowmeter for measuring fluid flow are disclosed. The invention combines isolating conditioner technology with ultrasonic technology to determine flow velocity. The method and apparatus of the invention does not require the use of integration techniques or the prior determination of flow swirl or asymmetry to achieve accuracy. The performance of this novel flowmeter exceeds the performance of current ultrasonic flowmeters by an order of four to twelve times and offers significant savings in manufacturing and maintenance costs. The disclosed flowmeter also has self-diagnostic capabilities.

The present continuation application claims the benefit of the filingdate of United States Utility Application Ser. No. 09/306,769, filed May7, 1999 now U.S. Pat. No. 6,494,105 (which is hereby incorporated byreference for all purposes).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of ultrasonic flowmeters and, inparticular, to an ultrasonic flowmeter that combines flow conditioningtechnology with simple and inexpensive ultrasonic technology to yieldhigh accuracy. The method and apparatus of the invention does notrequire the use of integration techniques or the prior determination offlow swirl or asymmetry to achieve accuracy. The invention also allowsimplementation of various self-diagnostic features.

2. Description of the Prior Art

Referring now to FIG. 1, flowmeters are generally classified as eitherenergy additive or energy extractive. Energy additive meters introduceenergy into the flowing stream to determine flowrate. Common examples ofenergy additive meters are magnetic meters and ultrasonic meters. Energyextractive meters require energy from the flowing stream, usually in theform of pressure drop, to determine the fluid's flowrate. Examples ofenergy extractive meters are PD meters, turbine meters, vortex metersand head meters (orifice, pitot, venturi, etc.).

Further subclasses of flowmeters are based on determining if the meteris discrete or inferential. Discrete meters determine the flowrate bycontinuously separating a flow stream into discrete segments andcounting them. Inferential meters infer flowrate by measuring somedynamic property of the flowing stream.

Ultrasonic flowmeters are energy additive inferential flowmeters. Theyare well known in the art and can be further subclassified as shown inFIG. 2. Ultrasonic flowmeters determine the velocity of the flowingstream from the difference in transit time of acoustic pulsestransmitted in the downstream and upstream directions between acoustictransducers. These acoustic pulses are transmitted along a chordal path,and a measure of the average chordal velocity is determined from themeasured transit times. The fluid can be gas or liquid.

Transit times depend on the mean velocity of the chordal path, the flowprofile and the turbulence structure of the flowing stream. Thereliability of the measured chordal velocity depends on the path length,the configuration and radial position of the acoustic path, thetransmitted acoustic pulse form, the electronic timing and gatingperformance and the calculations involved in reducing the measuredparameters to the mean chordal velocity.

Acoustic transducers can be mounted in an invasive or non-invasivemanner. An invasive mount invades the channel's containment structurethrough an aperture and allows the transducer to transmit acousticpulses directly into the flowing stream. Invasively mounted transducersare also referred to as “wetted” transducers. A non-invasive mounttransmits the acoustic pulses through all or part of the channel'scontainment structure. Transducers mounted in this fashion are alsoreferred to as “non-wetted” transducers.

The invasive mount is further classified as intrusive or non-intrusive.Intrusive mounting means that all or part of a transducer intrudes intothe flowing stream. Non-intrusive mounting means that the transducer isrecessed and does not intrude into the flowing stream.

Acoustic paths may be arranged in a reflective, non-reflective or hybridgeometry. A reflective path is arranged in a geometric manner to reflectone or more times off the containment structure or reflective bodiesinstalled inside the channel. A non-reflective path is arranged in ageometric manner that does not reflect off the containment structure ora reflective body inside the channel. A hybrid is a design that employsboth reflective and non-reflective paths. The number of paths and theirplacement in the channel vary among state of the art designs.

Ultrasonic flowmeters have been the center of attention within thenatural gas industry for the last decade. State of the art ultrasonicflowmeters employ one of two commercially available integration methodsto determine the average flow velocity in a circular duct. A thirdintegration method is under development by the scientific community.Both commercial methods perform well in the laboratory environment of“fully developed” pipe flow. However, in the industrial environment,multiple piping configurations assembled in series generate complexproblems for flow-metering engineers. The challenge is to minimize thedifference, i.e. achieve “similarity,” between the actual, field flowconditions and laboratory, “fully developed” flow conditions. Thecorrelating parameters which impact similarity vary with meter type anddesign. However, it is generally accepted that the level of sensitivityto time-averaged velocity profile, turbulence structure, and bulk swirlis dependent on the metering technology and the specific design of thatmeter.

The first integration method, known as Gaussian integration, is based ona fixed number of paths whose locations and correction factors are basedon the numerical Gaussian method selected by the designer. SeveralGaussian methods are available from publications (Jacobi & Gauss,Pannell & Evans, etc.) or disclosed in U.S. patents such as U.S. Pat.Nos. 3,564,912, 3,940,985, and 4,317,178. The advantages of thisapproach are clear. No additional information of the flow profile isrequired for calculating the average flowing velocity. The correctionfactors are fixed in advance as a result of the number of paths and theGaussian method selected by the designer. Gaussian integration methodsrequire at least four paths to yield acceptable results. Based onavailable public research, Gaussian integration methods have a biasuncertainty of up to 3% due to variations in piping configuration.

The second integration method, disclosed in U.S. Pat. No. 5,546,812,determines the swirl and asymmetry of the flowing stream by transmittingacoustic pulses along two or more paths having different degrees ofsensitivity to swirl and to symmetry. This method uses a conversionmatrix to determine the correction factors for the chordal velocitiesbased on the measured swirl and asymmetry. The recommended number ofpaths is five for the proprietary method. According to availableliterature, this integration method has an additional bias uncertaintyof up to 1% due to variations in piping configuration.

The third integration method, now under development by the NationalInstitute of Standards and Technology (NIST) is an eleven-patharrangement. The unit, termed the advanced ultrasonic flowmeter (AUFM),is based on computer modeling of pipe flow fields and simulations oftheir corresponding ultrasonic signatures. The sensor arrangement forthe AUFM will have enhanced velocity profile diagnostic capabilities fordeviations from non-ideal pipe flows. A pattern recognition systemcapable of classifying the approaching unknown flow among one of anumber of typical flows contained in an onboard, electronic library willinterpret the acoustic signals. The flow library will be created usingresults from computational fluid dynamics simulations. No biasuncertainty information is currently available for this experimentalintegration technique.

All of the state of the art ultrasonic flowmeters suffer from thedisadvantage of high cost due to the requirement of at least four paths(up to eleven paths in the AUFM). Each path requires a pair oftransducers with associated mounting mechanisms and wiring. Thus currentultrasonic flowmeters are costly and maintenance intensive. In addition,under real-world industrial conditions, current ultrasonic flowmeterssuffer relatively high bias uncertainty errors due to swirl andasymmetry effects. These disadvantages are overcome by the presentinvention.

SUMMARY OF THE INVENTION

The present invention combines simple ultrasonic technology withisolating flow conditioner technology to determine the flow velocity ina channel. The performance of this novel combination exceeds currentstate of the art ultrasonic flowmeter performance by an order of four totwelve times and offers significant savings in manufacturing costs. Inaddition, this novel device allows the creation of a method formeasuring the “real time” health of the flowmeter.

The isolating flow conditioner section of the present inventioneliminates swirl (defined as reducing swirl or radial velocityperpendicular to the direction of flow to less than 2 degrees) andeliminates asymmetry (defined as less than 5% difference in flowvelocity between parallel chords on opposing sides of the flow axis)upstream of the ultrasonic meter section. Acoustic pulses are thentransmitted along a chordal path within the conditioned flow and thechordal velocity is determined from the measured transit times. Acorrection factor is then applied to the “raw” chordal velocity todetermine a highly accurate “corrected” measure of chordal velocity. Thecorrection factor can be a weighting factor as further described below,or it can be a calibration factor based upon laboratory testing of thatparticular flowmeter. A calibration factor may be applied in lieu of theweighting factor or in addition to the weighting factor.

In designs that use a single-path ultrasonic flowmeter section, aweighting factor based upon the geometry of the acoustic path and theturbulence level of the flowing medium is used. Designs with anultrasonic flowmeter section that has more than one path can furtherrefine the weighting factor based upon a relaxation term, which is ameasure of flow profile development. Use of weighting factors provideshigh accuracy without the necessity for laboratory testing andcalibration of individual flowmeters.

A further advantage of the present invention is that the combination ofisolating flow conditioner technology with ultrasonic flowmetertechnology enables a self-diagnostic capabilities for measuring the“real time” health of the flowmeter. A one-path design provides alow-level capability for measuring flowmeter health, while multi-pathdesigns provide a high-level capability. In the industrial environment,a flowmeter with such built-in diagnostic capabilities is referred to asa “smart” flowmeter.

A further advantage of the present invention is that it can be used in avariety of different channel cross-sections, including cylindrical,square, rectangular, curved rectilinear or a U-shaped cross-sections,without any accuracy degradation.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 is a chart showing current classifications of flowmeters;

FIG. 2 is a chart showing current classifications of ultrasonicflowmeters;

FIG. 3 is a side view, not to scale, of an embodiment of the flowmeteraccording to the present invention;

FIG. 4 is a perspective view, not to scale, showing the installation ofalternative embodiments of the present invention in a pipe line;

FIG. 5A is a schematic diagram showing the test section used in theempirical tests of the flowmeter according to the present invention.

FIG. 5B is a schematic diagram showing the “Baseline” pipingconfiguration used for empirical tests of the flowmeter according to thepresent invention;

FIG. 5C is a schematic diagram showing the “T” piping configuration usedfor empirical tests of the flowmeter according to the present invention;

FIG. 5D is a schematic diagram showing the “Elbow+T” pipingconfiguration used for empirical tests of the flowmeter according to thepresent invention;

FIG. 6A is a side and end view of the first acoustic path used in thetest section for the empirical tests of the flowmeter according to thepresent invention;

FIG. 6B is a side and end view of the second acoustic path used in thetest section for the empirical tests of the flowmeter according to thepresent invention;

FIG. 6C is a side and end view of the third acoustic path used in thetest section for the empirical tests of the flowmeter according to thepresent invention;

FIGS. 7A-C are graphs showing the magnitude of one-path flowmeter errorfor various flow velocities.

FIGS. 8A-C are graphs showing the magnitude of two-path flowmeter errorfor various flow velocities.

FIGS. 9A-C are graphs showing the magnitude of three-path flowmetererror for various flow velocities.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 3 and 4, the present invention combines anisolating flow conditioner section 1 with an ultrasonic flowmetersection 2. The isolating flow conditioner section 1 of the presentinvention eliminates swirl (defined as reducing swirl or the ratio ofradial velocity to axial velocity to less than 2 degrees) and eliminatesasymmetry (defined as less than 5% difference in flow velocity betweenparallel chords on opposing sides of the flow centerline) upstream ofthe ultrasonic meter section 2. In the preferred embodiment, theisolating flow conditioner section 1 consists of an anti-swirl device 3followed by a profile device 4 as shown in FIGS. 3 and 4. However, theisolating flow conditioner section 1 could also consists of variouscombinations of other devices, such as nozzles, contractions, anti-swirldevices, profile devices, and static mixers. The important parameter forany combination is the elimination of swirl and the achievement ofaxisymmetrical flow (both as defined above).

Acoustic pulses 5 are transmitted along chordal path(s) in an ultrasonicflowmeter section 2 that is downstream of the isolating flow conditionersection 1. As the measurements occur within conditioned flow, the “raw”chordal velocity measurements determined from the measured transit timesare fairly accurate even without correction. However, the preferredembodiment improves accuracy even further by applying correction factorsto the “raw” chordal velocities to determine corrected chordalvelocities. The correction factors may be weighting factors (as definedbelow), calibration factors based upon actual laboratory testing of thespecific flowmeter, or a combination of weighting factors andcalibration factors. Application of calibration factors is only requiredwhere ultra-high accuracy is sought.

A fixed weighting factor based upon the geometry of the acoustic path(s)and the turbulence level of the flow can be used with any ultrasonicflowmeter section design. Designs with a multi-path ultrasonic flowmetersection that has at least two paths with differing geometries canfurther refine the weighting factor based upon a relaxation term, whichis a measure of flow profile development.

The preferred embodiment of the present invention also incorporatesself-diagnostic capabilities for measuring the “real time” health of theflowmeter. One-path and multi-path designs provides the following“low-level” self-diagnostic capabilities:

-   -   1. Comparison of the digital archives of the flowmeter during        dynamic calibration to the “real time” operation to determine        “key” anomalies;    -   2. Comparison of the operational digital archives of the        flowmeter to the “real time” operation to determine “key”        anomalies;    -   3. Timing clock stability based upon bias error from equation of        state's predicted velocity of sound and the actual measured        chordal velocity of sound;    -   4. Proper acoustic path lengths based upon bias error from        equation of state's predicted velocity of sound and the actual        measured chordal velocity of sound;    -   5. Proper programming associated with the calibration parameters        based upon bias error from equation of state's predicted        velocity of sound and the actual measured chordal velocity of        sound; and    -   6. Analysis of fluid variations or particulate deposits on the        containment structure, the invasive transducer's face, or the        mounting pockets based upon analysis of acoustic pulse train        strength or distortion and bias error from equation of state's        predicted velocity of sound and the actual measured chordal        velocity of sound.

A multi-path design provides the following additional “high-level”self-diagnostic capabilities:

-   -   1. Enhanced timing clock stability analysis based upon range        between the various chordal velocity of sound measurements;    -   2. Enhanced mechanical path angle analysis based upon: (a) range        between raw chordal velocities in parallel path geometries;        and/or (b) range between corrected chordal velocities in        parallel or non-parallel path geometries;    -   3. Enhanced acoustic path length analysis based upon: (a) range        between raw chordal velocities in parallel path geometries; (b)        range between corrected chordal velocities in parallel or        non-parallel path geometries; and/or (c) ratio between raw        chordal velocities in non-parallel geometric paths;    -   4. Enhanced calibration parameters programming analysis based        upon: (a) range between raw chordal velocities in parallel path        geometries; (b) range between corrected chordal velocities in        parallel or non-parallel path geometries; (c) ratio between raw        chordal velocities in non-parallel geometric paths; and/or (d)        range between chordal velocity of sound measurements;    -   5. Integration accuracy based upon: (a) range between raw        chordal velocities in parallel path geometries; (b) range        between corrected chordal velocities in parallel or non-parallel        path geometries; and/or (c) ratio between raw chordal velocities        in non-parallel geometric paths;    -   6. Proper electronics performance based upon: (a) range between        corrected chordal velocities in parallel or non-parallel path        geometries; and/or (b) range between chordal velocity of sound        measurements;    -   7. Proper acoustic probe performance based upon: (a) range        between corrected chordal velocities in parallel or non-parallel        path geometries; and/or (b) range between chordal velocity of        sound measurements;    -   8. Stability of delta time delays for each acoustic probe based        upon:(a) range between raw chordal velocities in parallel path        geometries; and/or (b) range between corrected chordal        velocities in parallel or non-parallel path geometries;    -   9. Signature recognition software based upon: (a) range between        raw chordal velocities in parallel path geometries; and/or (b)        range between corrected chordal velocities in parallel or        non-parallel path geometries; and    -   10. Enhanced analysis of fluid variations or particulate        deposits on the containment structure, the invasive transducer's        face or the mounting pocket based upon: (a) range between raw        chordal velocities in parallel path geometries; (b) range        between corrected chordal velocities in parallel or non-parallel        path geometries; and/or (c) ratio between raw chordal velocities        in non-parallel geometric paths.

All of these “real time” self-diagnostic health validations greatlyimprove the confidence in the performance of the flowmeter.

In the preferred embodiment, each chordal path has associated values forpath angle, path length, weighting factor and calibration factor. Alsoin the preferred embodiment, the following specifications are used asalarm points for the self-diagnostic tests:

-   -   1. Bias error from equation of state's predicted velocity of        sound and actual measured chordal velocity of sound should not        vary by more than 0.25%;    -   2. Range between chordal velocities in parallel path        geometry: (a) “raw” chordal velocities between non-reflective        chords in a parallel plane should not differ by more than 5%;        and (b) “raw” chordal velocities between reflective chords in        parallel planes should not differ by more than 2.5%;    -   3. Range between chordal velocities in parallel or non-parallel        geometric paths: (a) corrected chordal velocities between        non-reflective chords should not differ by more than 5%; and (b)        corrected chordal velocities between reflective chords should        not differ by more than 2.5%. Corrected chordal velocity refers        to chordal velocity computed by applying the path's weighting        factor, calibration factor, or weighting factor and calibration        factor to the “raw” chordal velocity measurement.

Referring now to FIG. 4, the flowmeter of the present invention can bebuilt into a pipeline by assembling various discrete segments containingthe isolating flow conditioner devices and the ultrasonic measuringdevices into the pipeline. In another embodiment, all of the devicesmaking up the flowmeter of the present invention are integrated into asingle flowmeter body that can be installed into a pipeline as a singlerobust unit.

The flowmeters according to the present invention were tested by anoutside research laboratory. Experiments were conducted with naturalgas. As shown in FIG. 5A, the experiments utilized a test sectionconsisting of a 10D isolating flow conditioner section 6, a 3D acousticsection 7, and a 5D exhaust section 8 (where D is the pipe diameter).The isolating flow conditioner 9 could be positioned anywhere within the10D isolating flow conditioner section 6 and was tested at 0D, 1D, 2D,3D, 4D, and 5D upstream of the acoustic section 7.

The acoustic section had three paths as shown in FIGS. 6A-6C. The firstpath (Path “A”), shown in FIG. 6A, was a double reflection, mid-radiuschord that appears as an inverted triangle in end view perspective. Thesecond path, shown in FIG. 6B (Path “B”), was a double reflection,mid-radius chord that appears as an upright triangle in end viewperspective. The third path, shown in FIG. 6C (Path “C”), was a singlereflection, centerline chord that appears as a bisecting line in endview perspective. All three paths were active during the tests. Byanalyzing each path separately and then in conjunction with other paths,each flow test simultaneously provided empirical data on single-pathmeters, two-path meters and three-path meters.

Three test loops were used, each designed to impart certaincharacteristics to the test section gas flow. As shown in FIG. 5B, the“Baseline” test loop flowed natural gas through a 90D section ofstraight pipe into the test section. This test loop providedfully-developed “laboratory” flow without swirl or asymmetry to the testsection. The “Tee” test loop, shown in FIG. 5C, attached the testsection directly to a pipe tee and provided asymmetric flow to the testsection. The “Elbow+Tee” test loop, shown in FIG. 5D, flowed natural gasthrough an elbow and a pipe tee out of plane to provide asymmetric andswirling flow to the test section.

Single Path Research

Using the above test loops, perturbation tests were conducted under thefollowing fluid dynamic conditions: (a) fully developed flow (FIG. 7A);(b) asymmetric, non-swirling flow (FIG. 7B); and (c) asymmetric,swirling flow (FIG. 7C). Multiple test runs were made with the isolatingflow conditioner located at various positions upstream from the acousticsection. Each test run spanned a range of flow velocities. For each flowvelocity and isolating flow conditioner location, residual error (“e”)values were plotted for Paths “A” (“Design ‘A’”) and “B” (“Design ‘B’”).Residual error is the difference between predicted weighting factor(“Yp”) and empirical weighting factor (“Ym”) as a percentage ofempirical weighting factor.

The predicted weighting factors were calculated according to the presentinvention. Each weighting factor included a path geometry term, and aturbulence term. For the single-path device, the relaxation term wasconstant due to the inability to measure relaxation absent more than onepath. Representative values are shown in the table below:

Baseline Test Loop Elbow + Tee Test Loop Path “A”/IFC @ 3D Path “B”/IFC@ 1D Path Geometry 0.8460 0.8460 Relaxation 0.1616 0.1616 Turbulence0.0010 0.0037 Predicted (“Yp”) 1.0086 1.0113 Empirical (“Ym”) 1.00921.0086 @ 67 fps Residual Error (“e”) −0.06% 0.27%Note that in the case of Path “A” and Path “B”, the path geometry termsare identical. This is because both paths are double reflection midradius chords. A differing path geometry would result in a differentpath geometry weighting factor.

The experiments demonstrated the validity of the novel concept. Thesingle-path device demonstrated a residual error of less than 0.5% withflow velocities greater than 5 feet per second. Since the empiricalweighting factor is based upon actual flow rate of the test loop, thismeans that the predicted weighting factors calculated according to thepresent invention produce measured flowrates that were within 0.5% ofthe actual flowrates in both perturbed and “laboratory” flow conditions.This performance, produced through the combination of effective flowconditioning and the application of accurate predicted weightingfactors, is far better than current state of the art Gaussianintegration flowmeters and equals the performance of five-pathproprietary integration flowmeters while using only one fifth of thetransducers and chordal paths. This results in considerable savings inmanufacturing and maintenance costs.

Multi-Path Research

Two-path and three-path performances were also analyzed based upon thepreviously described test runs. Two-path results are shown in FIGS. 8A(fully developed flow), 8B (asymmetric, non-swirling flow), and 8C(asymmetric, swirling flow). Likewise, three-path results are shown inFIGS. 9A (fully developed flow), 9B (asymmetric, non-swirling flow), and9C (asymmetric, swirling flow). In the two-path charts, for each flowvelocity and isolating flow conditioner location, residual error values(“e”) were plotted for Design “A” (combination of Path “A” and Path “C”)and Design “B” (combination of Path “B” and Path “C”). In the three-pathcharts, each residual error value (“e”) combines Paths “A,” “B,” and“C.”

The predicted weighting factors were calculated according to the presentinvention. Each weighting factor included a path geometry term, aturbulence term and a relaxation term. Representative values are shownin the tables below:

Two-Path Baseline Test Loop Design “A”/IFC @ 3D Path “A” Path “C” PathGeometry 0.8460 1.8245 Relaxation 0.1633 −0.8671 Turbulence 0.00100.0010 Predicted (“Yp”) 1.0103 0.9584 Empirical (“Ym”) 1.0105 0.9591 @42 fps Residual Error (“e”) −0.02% −0.07% Mean = −0.05% Elbow + Tee TestLoop Design “B”/IFC @ 1D Path “B” Path “C” Path Geometry 0.8460 1.8245Relaxation 0.1590 −0.8450 Turbulence 0.0037 0.0037 Predicted (“Yp”)1.0087 0.9832 Empirical (“Ym”) 1.0089 0.9834 @ 42 fps Residual Error(“e”) −0.02% −0.02% Mean = −0.02% Three-Path Tee Test Loop IFC @ 3D Path“A” Path “B” Path “C” Path Geometry 0.8460 0.8460 1.8245 Relaxation0.1578 0.1582 −0.8389 Turbulence 0.0010 0.0010 0.0010 Predicted (“Yp”)1.0048 1.0052 0.9866 Empirical (“Ym”) 1.0036 1.0063 0.9859 @ 14 fpsResidual Error (“e”) 0.12% −0.11% 0.07% Mean = 0.03%Note that in the above charts, the path turbulence terms are identical(0.0010 for tests with IFC @3D and 0.0037 for tests with IFC @1D). Thisis because the path turbulence term depends upon the distance of thepath from the isolating flow conditioner. Also note that unlike thesingle-path chart, the relaxation terms vary. This is because therelaxation term depends upon the actual relaxation of the flow asdetermined by the relationship between differing path velocitymeasurements. It takes at least two different paths with differing pathgeometries to measure and calculate a relaxation term.

The experiments demonstrated the validity of the novel concept. Thetwo-path device demonstrated a residual error of less than 0.25% withflow velocities greater than 5 feet per second. This means that thepredicted weighting factors calculated according to the presentinvention produce measured flowrates that are within 0.25% of the actualflowrates in both perturbed and “laboratory” flow conditions. Thisperformance exceeds the performance of all current integration-basedultrasonic flowmeters. Yet, this extraordinary performance is achievedusing less than half of the transducers and chordal paths with a relatedsavings in manufacturing and maintenance costs.

The three-path design performed even better and demonstrated a residualerror of less than 0.2% with flow velocities greater than 5 feet persecond.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means methods, or steps.

1. A flowmeter for measuring the flow of fluid in a channel, saidflowmeter comprising: (a) an isolating flow conditioner configured forinstallation in said channel for reducing flow swirl and asymmetry; (b)an ultrasonic measuring device configured for installation in thechannel downstream from said conditioner wherein said ultrasonicmeasuring device has at least one chordal path between acoustictransducers for measuring transit times of acoustic pulses; and (c) adigital microprocessor disposed in communication with said ultrasonicmeasuring device and configured to receive output from said ultrasonicmeasuring device and convert said output to a velocity measurement byapplying at least one correction factor selected from the group ofcorrection factors consisting of: a weighting factor based upon geometryof the chordal path, a weighting factor based upon flow turbulence, aweighting factor based upon flow relaxation, and combinations thereof.2. The flow meter of claim 1, wherein said flow conditioner isconfigured for reducing flow swirl to less than two degrees andasymmetry to less than 5% difference in flow velocity between a pair ofreference chords, said reference chords being on planes that arepositioned, in the channel, in mutual parallel relation and on oppositesides of the flow axis.
 3. The flowmeter of claim 2, wherein saidmicroprocessor is configured to convert said output to a velocitymeasurement by applying at least one correction factor that is aweighting factor based upon two or more chordal paths and flowturbulence.
 4. The flowmeter of claim 2, wherein said ultrasonicmeasuring device has at least two chordal paths and wherein saidmicroprocessor is configured to convert said output to a velocitymeasurement by applying at least one correction factor that is aweighting factor based upon chordal path, flow turbulence, and flowrelaxation.
 5. A method for analyzing the performance of an ultrasonicflowmeter, said method comprising the steps of: (a) reducing flow swirlto less than two degrees; (b) reducing flow asymmetry, such that thereis less than 5% difference in flow velocity between a pair of referencechords positioned respectively on a pair of mutually parallel planes andon opposite sides of the flow axis; (c) measuring transit times ofacoustic pulses along at least one chordal path within saidnon-swirling, axisymmetric flow; and (d) using said measured transittimes for obtaining a measured flow parameter used to perform at leastone self-diagnostic function.
 6. The method of claim 5, wherein saidstep of reducing flow asymmetry includes reducing flow asymmetry to lessthan 5% difference between any pair of parallel chords disposed onopposite sides of the flow axis.
 7. The method of claim 5, wherein saidstep of using said measured transit times includes performing saidself-diagnostic function to evaluate stability of a timing clock fromthe difference between a predicted velocity of sound based upon anequation of state and measured velocity of sound.
 8. The method of claim5, wherein said step of using said measured transit times includesperforming said self diagnostic function to evaluate acoustic pathlengths from the difference between a predicted velocity of sound basedupon an equation of state and measured velocity of sound.
 9. The methodof claim 5, wherein said step of using said measured transit timesincludes performing said self-diagnostic function to evaluate fluidvariations from the difference between a predicted velocity of soundbased upon an equation of state and measured velocity of sound.
 10. Themethod of claim 5, wherein said step of using said measured transittimes includes performing said self-diagnostic function to evaluatefluid variations based upon an analysis of distortion or strength ofsaid acoustic pulse.
 11. The method of claim 5, wherein said step ofusing said measured transit times includes performing saidself-diagnostic function to evaluate particulate deposits on thechannel's containment structure, an acoustic transducer's face, or anacoustic transducer's mounting pocket based upon an analysis ofdistortion or strength of said acoustic pulse.
 12. The method of claim5, wherein said measuring step includes using at least two chordal pathsand said step of using said measured transit times includes performingsaid self-diagnostic function to evaluate stability of a timing clockfrom the difference between at least two chordal paths' velocity ofsound measurements.
 13. The method of claim 5, wherein said measuringstep includes using at least two chordal paths and said step of usingsaid measured transit times includes performing said self-diagnosticfunction to evaluate at least one mechanical path angle from thedifference between at least two chordal paths' corrected velocities. 14.The method of claim 5, wherein said measuring step includes using atleast two chordal paths of parallel geometry and said step of using saidmeasured transit times includes performing said self-diagnostic functionto evaluate at least one acoustic path's length from the differencebetween at least two chordal paths' raw velocities.
 15. The method ofclaim 5, wherein said measuring step includes using at least two chordalpaths and said step of using said measured transit times includesperforming said self-diagnostic function to evaluate calibrationparameter programming from the difference between at least two chordalpaths' corrected velocities.
 16. The method of claim 5, wherein saidmeasuring step includes using at least two chordal paths and said stepof using said measured transit times includes performing saidself-diagnostic function to evaluate calibration parameter programmingfrom the difference between at least two chordal paths' velocity ofsound measurements.
 17. The method of claim 5, wherein said measuringstep includes using at least two chordal paths and said step of usingsaid measured transit times includes performing said self-diagnosticfunction to evaluate integration accuracy from the difference between atleast two chordal paths' corrected velocities.
 18. The method of claim5, wherein said measuring step includes using at least two chordal pathsand said step of using said measured transit times includes performingsaid self-diagnostic function to evaluate electronics performance fromthe difference between at least two chordal paths' corrected velocities.19. The method of claim 5, wherein said measuring step includes using atleast two chordal paths and said step of using said measured transittimes includes performing said self-diagnostic function to evaluateelectronics performance from the difference between at least two chordalpaths' velocity of sound measurements.
 20. The method of claim 5,wherein said measuring step includes using at least two chordal pathsand said step of using said measured transit times includes performingsaid self-diagnostic function to evaluate acoustic probe performancefrom the difference between at least two chordal paths' correctedvelocities.
 21. The method of claim 5, wherein said measuring stepincludes using at least two chordal paths and said step of using saidmeasured transit times includes performing said self-diagnostic functionto evaluate acoustic probe performance from the difference between atleast two chordal paths' velocity of sound measurements.
 22. The methodof claim 5, wherein said measuring step includes using at least twochordal paths of parallel geometry and said step of using said measuredtransit times includes performing said self-diagnostic function toevaluate delta time delay stability from the difference between at leasttwo chordal paths' raw velocities.
 23. The method of claim 5, whereinsaid measuring step includes using at least two chordal paths and saidstep of using said measured transit times includes performing saidself-diagnostic function to evaluate delta time delay stability from thedifference between at least two chordal paths' corrected velocities. 24.The method of claim 5, wherein said measuring step includes using atleast two chordal paths of parallel geometry and said step of using saidmeasured transit times includes performing said self-diagnostic functionto evaluate device signature from the difference between at least twochordal paths' raw velocities.
 25. The method of claim 5, wherein saidmeasuring step includes using at least two chordal paths and said stepof using said measured transit times includes performing saidself-diagnostic function to evaluate device signature from thedifference between at least two chordal paths' corrected velocities. 26.The method of claim 5, wherein said measuring step includes using atleast two chordal paths and said step of using said measured transittimes includes performing said self-diagnostic function to evaluatefluid variations from the difference between at least two chordal paths'corrected velocities.
 27. The method of claim 5, wherein said measuringstep includes using at least two chordal paths of parallel geometry andsaid step of using said measured transit times includes performing saidself-diagnostic function to evaluate particulate deposits on thechannel's containment structure, an acoustic transducer's face, or anacoustic transducer's mounting pocket from the difference between atleast two chordal paths' raw velocities.
 28. The method of claim 5,wherein said measuring step includes using at least two chordal pathsand said step of using said measured transit times includes performingsaid self-diagnostic function to evaluate particulate deposits on thechannel's containment structure, an acoustic transducer's face, or anacoustic transducer's mounting pocket from the difference between atleast two chordal paths' corrected velocities.
 29. A flowmeter formeasuring the flow of fluid in a channel, said flowmeter comprising: (a)an isolating flow conditioner for eliminating flow swirl and asymmetry;(b) an ultrasonic measuring device installed in said channel downstreamfrom said conditioner wherein said ultrasonic measuring device has atleast one chordal path between acoustic transducers for measuringtransit times of acoustic pulses; (c) a digital microprocessor disposedin communication with said ultrasonic measuring device and configured toreceive output from said ultrasonic measuring device and convert saidoutput to a velocity measurement by applying at least one correctionfactor selected from the group of correction factors consisting of: aweighting factor based upon geometry of the chordal path, a weightingfactor based upon flow turbulence, a weighting factor based upon flowrelaxation, and combinations thereof; and (d) self-diagnostic softwarewithin said digital microprocessor programmed to use a measured flowparameter for the performance of at least one self-diagnostic function.30. The flowmeter of claim 29, wherein said software is programmed forthe performance of a self-diagnostic function based on the differencebetween a predicted velocity of sound based upon an equation of stateand measured velocity of sound.
 31. The flowmeter of claim 30, whereinsaid software is programmed for the performance of a self-diagnosticfunction selected from the group of self-diagnostic capabilitiesconsisting of: evaluate at least one acoustic path's length; evaluatestability of a timing clock; evaluate fluid variations; and combinationsthereof.
 32. The flowmeter of claim 29, wherein said ultrasonicmeasuring device has at least two chordal paths and said software isprogrammed for the performance of a self-diagnostic function based onthe difference between at least two chordal paths' velocity properties.33. The flowmeter of claim 32, wherein at least two chordal paths'corrected velocities is selected from the group consisting of: rawvelocities; corrected velocities; velocity of sound measurements; andcombinations thereof.
 34. The flowmeter of claim 33, wherein saidsoftware is programmed for the performance of a self-diagnostic functionto evaluate calibration parameter programming.
 35. The flowmeter ofclaim 33, wherein said ultrasonic measuring device has at least twochordal paths and said software is programmed for the performance of aself-diagnostic function to evaluate at least one acoustic path'slength.
 36. The flowmeter of claim 33, wherein said software isprogrammed for the performance of a self-diagnostic function to evaluateintegration accuracy from the difference between at least two chordalpaths' corrected velocities.
 37. The flowmeter of claim 33, wherein saidsoftware is programmed for the performance of a self-diagnostic functionto evaluate electronics performance.
 38. The flowmeter of claim 33,wherein said software is programmed for the performance of aself-diagnostic function to evaluate acoustic probe performance.
 39. Theflowmeter of claim 33, wherein said software is programmed for theperformance of a self-diagnostic function to evaluate delta time delaystability.
 40. The flowmeter of claim 33, wherein said software isprogrammed for the performance of a self-diagnostic function to evaluatedevice signature.
 41. The flowmeter of claim 29, wherein said softwareis programmed for the performance of a self-diagnostic function toevaluate particulate deposits on the channel's containment structure, anacoustic transducer's face, or an acoustic transducer's mounting pocketfrom the difference between at least two chordal paths' raw or correctedvelocities.
 42. The flowmeter of claim 29, wherein said measured flowparameter is selected from the group of flow parameters consisting of:measured velocity of sound, distortion of said acoustic pulse, strengthof acoustic pulse, chordal path velocity, and combinations thereof.